1. Field of the Invention
The present invention relates to axial pumps, and more specifically, to axial pumps driven by piezoelectric torsional vibration driven motors.
2. Description of the Background Art
The use of piezoelectric ceramic materials such as lead zirconate titanate (PZT) is well known for applications for sensors, transducers, actuators, and other electromechanical devices.
Many actuators have been developed using electroactive materials, including the torsional actuator disclosed in U.S. Pat. No. 6,020,674. This torsional actuator uses an even number of alternately poled segments of electroactive material which are arranged side by side. The segments are bound together in an integral structure, with conductors positioned between adjacent segments. Under an applied electric field, the torsional actuator produces large angular displacement and a high torque. Similarly, a torsional piezoelectric actuator is described in Glazounov, A. E. Zhang, Q. M., Kim, C. xe2x80x9cPiezoelectric Actuator Generating Torsional Displacement from Piezoelectric d15 Shear Responsexe2x80x9d Applied Physics Letters 72, pages 2526-2528, 1998.
For some applications, a large rotational motion with a large torque output is demanded. For example, vibration and noise control systems for helicopter rotor blades require an actuator which can provide large amplitude rotational motion with a high torque.
Piezoelectric ultrasonic motors have been developed using traveling wave and standing wave theories which provide higher torque density than electromagnetic motors. An example of the current art in piezoelectric motor technology is provided in xe2x80x9cDevelopment of a Two-Sided Piezoelectric Rotary Motor for High Torquexe2x80x9d, T. S. Glenn, W. G. Hagwood, SPIE Volume 3041, 1997. These piezoelectric ultrasonic motors are of limited application, however, because they have either lower power density or lower efficiency than conventional electromagnetic motors.
A compact, simple, lightweight motor which uses a torsional actuator as a stator could provide high torque density, high power density, and high efficiency in response to an alternating electric field.
Axial flow pumps with moving shafts within stationary housings are well known in the art for transferring liquids, granular solids, gases, and slurries. These pumps are may be powered by different power sources.
As opposed to most axial flow pumps that operate with moving shafts within stationary housings, the new pump disclosed and claimed operates with helical fan blades attached within the moving housing as a shaft. The shaft is driven by a piezoelectric torsional actuator as described in U.S. Pat. No. 6,020,674, which is incorporated by reference here, and U.S. patent application Ser. No. 09/697,716 claiming priority to provisional application 06/162527 filed Oct. 27, 1999.
It is an object of this invention to provide an axial bidirectional flow pump driven by a full cycle piezoelectric torsional motor which is compact, light, and a high power density device.